1. Field of the Invention
The present invention relates to a telephone subscriber loop overvoltage protection circuit and, more particularly, to an overvoltage protector which is fully integrated and is capable of accommodating overvoltages of, for example, 210-265 V.
2. Description of the Prior Art
Communication lines may carry foreign electrical energy from many sources, for example, lightning strikes and power transmission line faults. In order to safeguard communication equipment connected to such lines, prior protection circuits have included large numbers of discrete components.
More recently, switching or crowbar type protection circuits have been developed which include semiconductor elements. Such circuits, however, may not be adapted to the specialized protection requirements of communication circuits. A communication protector should be resistant to latching due to the constant DC current supplied by a central office. In addition, if foreign voltage appears between one conductor and ground of a two conductor communication line, it is also desirable to provide balanced protection by grounding both conductors. Further, modern construction trends toward out-of-sight equipment installation urge that a protector by physically compact as well.
It is therefore an object of the invention to provide an arrangement affording overvoltage protection for three-wire telephone subscriber loops which is fully integrated and able to perform the desired protection functions.